EVOLUTION OF ENERGY-CONTAINING TURBULENT EDDIES IN THE SOLAR-WIND

Previous theoretical treatments of fluid-scale turbulence in the solar wind have concentrated on describing the state and dynamical evolutio n of fluctuations in the inertial range, which are characterized by po wer law energy spectra. In the present paper a model for the evolution of somewhat larger, more energetic magnetohydrodynamic (MHD) fluctuat ions is developed by analogy with classical hydrodynamic turbulence in the quasi-equilibrium range. The model is constructed by assembling a nd extending existing phenomenologies of homogeneous MHD turbulence, a s well as simple two-length-scale models for transport of MHD turbulen ce in a weakly inhomogeneous medium. A set of equations is presented f or the evolution of the turbulence, including the transport and nonlin ear evolution of magnetic and kinetic energy, cross helicity, and thei r correlation scales. Two versions of the model are derived, depending on whether the fluctuations are distributed isotropically in three di mensions or restricted to the two-dimensional plane perpendicular to t he mean magnetic field. This model includes a number of potentially im portant physical effects that have been neglected in previous discussi ons of transport of solar wind turbulence. Numerical solutions are sho wn for several cases of interest that demonstrate the advantages of th is approach. We suggest that this model may prove useful in studies of solar wind heating and acceleration, as well as in describing the res ponse of interplanetary turbulence to wave energy injected by pickup i ons and planetary upstream waves.